Manufacture of 2-anthrahydroquinone-carboxylic acid



Patented July 20, 1948 UNITED OFFICE MANI'IFAGTUBE OF 2-ANTHRAHXDROQUI- NONE-CARBOXYLIG AGID' J Sweet, Aurora, N. Y a'ss'ig'nur "to Allied chemical and Dye permeation,- New York, N. Y., a. corporation fif'Ne-W York No Application- Dcfober 9,1913, Serial No. 702,085

5 Glaims.

invention relates to the manufacture or 2- anthrahy-droquinone carboxylic acid and relates articmariy 110' an improveu'method 6f TedfiCi-illgsblhinders the reaction of the salt withthe g agent. The '2-anthrahydroquinone-carb'o'i cylio acid obtained by alkaline reduction has a fiufiy, bulky physical structure. In aqueous suspendon containing as little as- 2% solids (by Wei ht), the reduction product terms a thick, pasty slurry which is 'difii'cult to agitate and filter,

afr'iel yields a filter cake which is bulky, retains large amounts of liquid, and the wet state readily oxidizes on exposure to "air even at room temperature. To avoid excessive oxidation of this le'uco icr'm during drying, the bulky filter cake mastnez undergo more than limited exposure to air and must be dried in vaeuc; earing drying, the material must be broker-1 up repeatedly to prevent formation of partially oxidized skin's which inhibit the drying of the under-- lying leuco compound. These disadvantages in the alkaline reduction process necessitate s'm'all batches, long process cycles, and special handling and drying precautions, which in the -'a-"ggreg ai'ie result in a relatively high cost of manufacture.

It is an object or the present invention 'to prov'ide an improved process for the manufacture of Q- arithrahydroquinone carboiiylic acid by means of hydrosulfite. A further objeet' is to provide a reduction process which can be conducted at relatively high concentrations without special handling equipment. A further object is to provide a product in such form that filtration and draining are rapid, efficient, and relatively complete. A further object is to :provide a product which is less readily oxidized by contact with air and which, as a result of this property, plus its excellent drainage characteristics, can be worked up without special precautions to prevent access of air.

In accordance with the present invention, 2- anthraquinone-carboxylic acid is reacted with an aqueous hydrosulfite reducing solution at a or less than 5.

Bymaintaihin'g the hy'drofsuliite reducing solution-sufiici'enuy acid, the ZZ an'thraquinOne CaF boxylic acid and its reductionproduct are re taine'd "substantially entirely in solid phase and it is p'os'si bl'eto effect the reductionat substantially greater concentrations of anthraquinone carboxylate, and to obtain a i reduct which product is produced in the form of an aqueous sbll'iti'oh of the alkali-metal salt;

The reduction may be carried out satisfact'oriiy wit ratios of anthraquinone carboxylic acid towater between 3% and 10% by weight.

The concentration is not critical and concentra tion's"out'side this rangeina be used; However, concentrations "of 'anthraquinone 'carboxylic aeitl in excess of trie range' peeifiea-resuit in verythiek slurr'ies and with 'such concentrations it is ad visabie to use equi ment especially adapteafror handling heav "sluiries. concentrations below the range specified merely increase the bulk of the reaction mixture and reduce the capacity of theequipment for productio (if-finished product. A suspension of about '6' part's of anthraquinonecarboxylic acid per 100 parts by Weight of water provides the preferred concentration.

The amount or hydrosulfite used may be varied in accordancewith the desired degree or reduction of the 2-'anthraquinone-carboxylic acid. For some purposes (for example, to accelerate the bodyin'g' bfli'tiseedhil by boiling) a mixture con-- sisting" of '2=arithraquinone-earboxy1ic acid and its leuco compound, such as the product of Example 2 below, is suitable'andeffecti e. For fpurp'oses'oi dyestuffrnanufacture;whena more complete reduction "is desirable, the stoic'liio'metric or aereateramuuni'oi "hydrosulfite may be used. In all cases the "acid reduction is rapid and the 2-"- antlirahydroquinonerartoxsdia acid is lessbulky, more iilterab'le and less prone to an oxidation than the alkaline-reduced product.

It is preferred to conduct the reduction withhydrosulfite at a solution pH between 0.1 and 4.5 and at a temperature between 50 C. and 70 C., and especially between C. and C. in order to obtain a rapid reduction and provide a product of most satisfactory physical character.

The following examples further illustrate the invention. Proportions are in terms of weight unless otherwise indicated.

Example 1 A mixture of 100 parts of 2-anthraquinonecarboxylic acid and 1650 parts of water was heated with agitation to about 60 C. and to the agitated slurry 50 parts of sodium hydrosulfite (anhydrous) was added in a period of about one minute. The solution pH was approximately 4.2 at both the beginning and end of the addition. The white color of the slurry changed immediately to a dark color which proceeded gradually from brown to greenish-black at the end of the hydrosulfite addition. The slurry was then cooled to 30 C. and filtered. The filter cake was washed with 200 parts of Water. Both filtering and washing occupied a total time of one minute.

amounted to 290 parts containing 98 parts of product (dry basis).

Th same process was carried out by adding an aqueous solution of 50 parts of sodium hydrosulfite and 100 parts of sodium hydroxide in 1000 parts of water to the carboxylic acid slurry. However, when the process was carried out with less than 4800 parts of water the final acid slurry was so thick that it could not be handled. and hence in this instance 4800 parts of water was employed instead of the 1650 parts employed in the acid reaction to secure a fluid slurry. Except asindicated the reduction was carried out in just the same manner as before. At the end of the reduction, the solution of the product was acidified with aqueous 20 B (32%) muriatic acid to a pH of 1.5 to precipitate the Z-anthrahydroquinone-carboxylic acid. The resulting slurry was then filtered as in the case of the acid reduction. However, filtration was so slow that 1%, hours was required for filtration and washing, as compared to one minute for the acid-reduced product. The filter cake, after filtering and washing, amounted to 1350 parts containing 98 parts of product (dry basis). Thus the filter-cake contained over 1000 parts more of water than the filter-cake obtained in the acid-reduction process.

Example 2 An aqueous paste containing 62 parts of finely divided 2-anthraquinone-carboxylic acid was stirred into about 1000 parts of water. The mix ture was agitated and heated to about 60 C. To the warm slurry, 31 parts of sodium hydrosulfite was added. The white or cream color of the slurry immediately changed to a dark color ranging from brown to greenish-black, as is customary in this reduction. The slurry'was then cooled to 30 C. and filtered. The filtration Was rapid and the filter cake comprising Z-anthrahydroquinone-carboxylic acid and unreduced 2-anthraquinone--carboxylic acid was dense, but was porous enough to let mother liquor and water washes pass through it readily. The cake containing about 25% solids was dried below 70 C. in an air drier. The dry product was soluble in aqueous caustic soda, thus showing that it was chiefly the leuco form of the Z-anthraquinonecarboxylic acid. I

The filter cake, weighed immediately without drying,

4 Example 3 123 parts of an aqueous paste of Z-anthraquinone-carboxylic acid, which by analysis contained 39% of the acid, was suspended in 1000 parts of water. To the resulting uniform agitated slurry, heated to about 60 C., 42 parts sodium hydrosulfite (anhydrous) was added. The mixture rapidly turned black and finally changed to a grayish-brown slurry, which was cooled to about 30 C., and filtered. The precipitate formed a dense, compact, porous filter cake, which was easily washed with cold water until the washings were free from inorganic salts. The filter cake was then dried in an air oven at a temperature slightly below 65 C. The dry product (44 parts) was a light-gray solid, soluble in dilute aqueous I caustic soda, to yield a red solution which, on

standing, oxidized to a white precipitate.

In a melting point tube, the product changed at a temperature between C. and C. from a gray to a light yellow compound which melted at about 275 C. and was no longer soluble in aqueous caustic soda, thus showing that on heating, the leuco compound had oxidized to 2-anthraquinone-carboxylic acid.

I claim:

1. The method of making 2-anthrahydroquinone-carboxylie acid, which comprises reacting 2-anthraquinone-carboxylic acid with aqueous hydrosulfite reducing solution at a pH of les than 5.

2. The method of making 2-anthrahydroquinone-carboxylic acid, which comprises reacting 2-anthraquinone-carboxylic acid with aqueous hydrosulfite reducing solution at a temperature between 50 and 70 C. at a pH sufficiently low to prevent solution of asubstantial proportion of the Z-anthrahydroquinone carboxylic acid product.

3. The method of making 2-anthrahydroquinone-carboxylic acid directly in solid phase, which comprises agitating 2-anthraquinonecarboxylic acid in aqueous hydrosulfite reducing solution at a pH of less than 5, the ratio of carboxylic acid to water being between 3% and 10%.

4. The method of making 2-anthrahydroquinone-carboxylic acid directly in solid phase, which comprises agitating 2-anthraquinone-carboxylic acid in aqueous hydrosulfite reducing solution at a pH of less than 5 and at a temperature between 50 and 70 0., th ratio of the carboxylic acid to water being between 3% and 10%.

5. The method of making Z-anthrahydroquinone-carboxylic acid directly in solid phase, which comprises agitating Z-anthraquinonecarboxylic acid in aqueous hydrosulfite reducing solution at a pH between and 4 at a solution temperature between 50 and 70 0., the ratio of the carboxylic acid to water being between 3% and 10%.

' ALVIN J. SWEET.

REFERENCES CITED The following references are of record in the file of this patent:

Fierz-David Kunstliche Organische Farbstofie (1926) page 691. 

